Plant and Soil

, Volume 97, Issue 1, pp 3–13

Seasonal N2 fixation by cool-season pulses based on several15N methods

  • S. C. Smith
  • D. F. Bezdicek
  • R. F. Turco
  • H. H. Cheng
Article

DOI: 10.1007/BF02149818

Cite this article as:
Smith, S.C., Bezdicek, D.F., Turco, R.F. et al. Plant Soil (1987) 97: 3. doi:10.1007/BF02149818

Summary

Accurate estimates of N2 fixation by legumes are requisite to determine their net contribution of fixed N2 to the soil N pool. However, estimates of N2 fixation derived with the traditional15N methods of isotope dilution and AN value are costly.

Field experiments utilizing15N-enriched (NH4)2SO4 were conducted to evaluate a modified difference method for determining N2 fixation by fababean, lentil, Alaska pea, Austrian winter pea, blue lupin and chickpea, and to quantify their net contribution of fixed N2 to the soil N pool. Spring wheat and non-nodulated chickpea, each fertilized with two N rates, were utilized as non-fixing controls.

Estimates of N2 fixation based on the two control crops were similar. Increasing the N rate to the controls reduced AN values 32, 18 and 43% respectively in 1981, 1982 and 1983 resulting in greater N2 fixation estimates. Mean seasonal N2 fixation by fababean, lentil and Austrian winter pea was near 80 kg N ha−1, pea and blue lupin near 60 kg N ha−1, and chickpea less than 10 kg N ha−1. The net effects of the legume crops on the soil N pool ranged from a 70 kg N ha−1 input by lentil in 1982, to a removal of 48 kg N ha−1 by chickpea in 1983.

Estimates of N2 fixation obtained by the proposed modified difference method approximate those derived by the isotope dilution technique, are determined with less cost, and are more reliable than the total plant N procedure.

Key words

AN valueIsotope dilution15NN balanceN2 fixationSoil nitrogen

Copyright information

© Martinus Nijhoff Publishers 1987

Authors and Affiliations

  • S. C. Smith
    • 1
  • D. F. Bezdicek
    • 1
  • R. F. Turco
    • 1
  • H. H. Cheng
    • 1
  1. 1.Department of Agronomy and SoilsWashington State UniversityPullmanUSA
  2. 2.Earth Sciences DepartmentBattelle Pacific Northwest LaboratoriesRichlandUSA